1. Field of the Invention
The present invention relates to a method and apparatus for measurement of an eccentricity dimension which can measure the eccentricity dimension between, for example, fibers of a ribbon-shaped optical fiber comprised of a plurality of optical fibers covered with a coating member and a fiber ribbon. The present invention also relates to an apparatus for control of the eccentricity dimension which uses the method for measurement of the eccentricity dimension and feeds back the measured results so as to obtain a fiber ribbon uniformly covered with the coating member. The present invention further relates to a method and system for manufacturing a ribbon-shaped optical fiber having an even shape.
2. Description of the Related Art
Known in the art is a ribbon-type optical fiber (hereinafter referred to as a "fiber ribbon") comprised of a plurality of optical fibers arranged in a row or several layers and covered on their outside with a resin material or the like. This covering of the coating member is performed by supplying an uncured resin to a cavity formed inside a coating die while pulling the optical fibers orderly from a plurality of supply drums and passing them through the coating die. Prevention of deviation of the center positions of the optical fibers and fiber ribbon (hereinafter referred to as the "eccentricity" or the "eccentricity dimension") is an important factor in manufacture.
For example, when removing the coating member to connect optical fibers by using a peeling tool, if the eccentricity dimension exists, the optical fibers can be damaged by the peeling tool.
In the part, the thickness t of the fiber ribbon 1 shown in FIGS. 1A and 1B was measured using for example a laser dimension meter, but the eccentricity dimension .alpha. had been measured by destructive testing, that is, by cutting the end of the fiber ribbon 1 manufactured and examining the cross-section by a microscope or the like.
If it were possible to measure the eccentricity dimension .alpha. in-line over the entire length of a long fiber ribbon 1 in its longitudinal direction, then, for example, the results of measurement could be sequentially fed back so as to adjust the manufacture and control the eccentricity dimension .alpha. to "0". As a result, it would be possible to manufacture a fiber ribbon 1 with a coating member 2 formed to a uniform thickness (t.sub.u =t.sub.t).
The conventional method of measurement of the eccentricity dimension explained above, however, was a destructive test method, so it was only possible to measure the eccentricity dimension .alpha. at the two ends of the fiber ribbon 1. Even if the eccentricity dimensions .alpha. of the two ends were within the range of required values, it could not be guaranteed that the center portion of the fiber ribbon 1 was being manufactured within the range of standard values.
Further, in the conventional method of measurement by destructive testing, in-line measurement was not possible and the results of measurement could only be obtained after the manufacture, so the quality of the product 1 was learned only after the fiber ribbon 1 finished being covered. Accordingly, when the eccentricity dimension .alpha. fell out of the range of required values, it was necessary to discard the entire long fiber ribbon 1 or take similar action.
Japanese Unexamined Patent Publication (Kokai) 3-253806 (JPP3-253806) discloses a method of inspecting an eccentricity dimension .alpha. of resin coating of a fiber ribbon, in which optical fibers coated with resin are bent reversely by two guide rollers, two tension forces at the guide rollers are detected, and the eccentricity dimension of the resin coating is detected on the basis of difference between the two forces. The method disclosed in JPP 3-253806 is an on-line and non-destructive test, and therefore, can overcome the above disadvantages in the destructive test.
However, JPP 3-253806 does not disclose an explicit algorithm and equations for calculating the eccentricity dimension and, thus, is merely an idea.
Further, the measurement of the tension forces in JPP 3-253806 is difficult and inaccurate, and thus correct detection of the eccentricity dimension can not be achieved.